DESCRIPTION: Idiopathic pulmonary arterial hypertension (IPAH) is a severe form of pulmonary arterial hypertension (PAH) characterized by progressive remodeling of the pulmonary vasculature, resulting in elevated pulmonary vascular resistance and eventually leading to right heart failure and death (16). IPAH is incurable and the cause of the disease is unknown. Increasing evidence suggests that there are major intrinsic changes in Ca2+ homeostasis of IPAH-PASMCs that may involve multiple Ca2+ pathways. The goal of our research is to elucidate the regulatory mechanisms of the Ca2+ pathways responsible for the pathologic changes of Ca2+ homeostasis in PASMCs during IPAH. The transient receptor potential (TRP) gene superfamily encodes a large repertoire of non-selective ion channels with diverse physiological functions. Many of these channels have been detected in human PASMCs. Previous studies have found an upregulation of TRPC3 and TRPC6 expression in IPAH-PASMCs; a functional single nucleotide polymorphism of TRPC6 has also found in these cells. Our previous studies also show that that TRPC1 and TRPC6 expression are upregulated, and store- operated (SOCE) and receptor-operated Ca2+ entry (ROCE) are enhanced in PASMCs of chronic hypoxic and monocrotaline-induced PH rats. Moverover, the mechanosensitive TRPV4 channel is also up-regulated and mechanosensitive cation entry (MSCE) is enhanced in PASMCs of chronic hypoxia rats. Even though no animal model can recapitulate human IPAH, these results suggest that alterations in multiple TRP-dependent pathways may contribute to the development of PH. However, the expression and the pathophysiological functions of many TRP channels (TRPC, TRPV and TRPM subfamilies) have not been investigated systematically in IPAH-PASMCs. In this application, we propose that the expression of multiple TRPC, TRPV, and TRPM channels are intrinsically altered in IPAH-PASMCs, and these changes contribute significantly to the aberrant phenotypes of these vascular myocytes. To test this hypothesis, we will apply a combination of Ca2+ imaging, patch clamping, and siRNA gene knockdown and over-expression techniques on human PASMCs cultured from main elastic arteries, type I - III small pulmonary arteries of control and IPAH lung provided by the Pulmonary Hypertension Breakthrough Initiative (PHBI) to: (1) identify the TRP channels with their expression altered in IPAH-PASMCs; (2) determine the TRP channels responsible for the altered SOCE, ROCE and MSCE in IPAH-PASMCs; and (3) determine the TRP channels contribute to the enhanced proliferation of IPAH-PASMCs. The proposed experiments will identify the full complement of TRP channel dependent pathways that are responsible for the intrinsic differences in Ca2+ signaling in IPAH-PASMCs. These results are expected to have important positive impact because the novel mechanistic information on the pathophysiology of IPAH may help to identify new therapeutic targets for the treatments of this deadly disease.